New design based on *mut T

Cargo.toml

@@ -14,6 +14,9 @@ repository = "https://github.com/rust-osdev/volatile"
 # Enable unstable features; requires Rust nightly; might break on compiler updates
 unstable = []
 
+[dev-dependencies]
+rand = "0.8.3"
+
 [package.metadata.release]
 no-dev-version = true
 pre-release-replacements = [

src/access.rs

@@ -1,22 +1,56 @@
+pub trait Access {}
+
 /// Helper trait that is implemented by [`ReadWrite`] and [`ReadOnly`].
-pub trait Readable {}
+pub trait Readable: UnsafelyReadable {}
 
 /// Helper trait that is implemented by [`ReadWrite`] and [`WriteOnly`].
-pub trait Writable {}
+pub trait Writable: UnsafelyWritable {}
+
+pub trait UnsafelyReadable {}
+
+pub trait UnsafelyWritable {}
 
 /// Zero-sized marker type for allowing both read and write access.
 #[derive(Debug, Copy, Clone)]
 pub struct ReadWrite;
+impl Access for ReadWrite {}
 impl Readable for ReadWrite {}
+impl UnsafelyReadable for ReadWrite {}
 impl Writable for ReadWrite {}
+impl UnsafelyWritable for ReadWrite {}
 
 /// Zero-sized marker type for allowing only read access.
 #[derive(Debug, Copy, Clone)]
 pub struct ReadOnly;
 
+impl Access for ReadOnly {}
 impl Readable for ReadOnly {}
+impl UnsafelyReadable for ReadOnly {}
 
 /// Zero-sized marker type for allowing only write access.
 #[derive(Debug, Copy, Clone)]
 pub struct WriteOnly;
+
+impl Access for WriteOnly {}
 impl Writable for WriteOnly {}
+impl UnsafelyWritable for WriteOnly {}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Custom<R, W> {
+    pub read: R,
+    pub write: W,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct NoAccess;
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct SafeAccess;
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct UnsafeAccess;
+
+impl<W> Readable for Custom<SafeAccess, W> {}
+impl<W> UnsafelyReadable for Custom<SafeAccess, W> {}
+impl<W> UnsafelyReadable for Custom<UnsafeAccess, W> {}
+impl<R> Writable for Custom<R, SafeAccess> {}
+impl<R> UnsafelyWritable for Custom<R, SafeAccess> {}
+impl<R> UnsafelyWritable for Custom<R, UnsafeAccess> {}